Die casting of core windings



Nov. 4, 1969 K. CLARK ET AL 3,477,051

DIE CASTING OF CORE WINDINGS Filed Jan. 15, 1968 4 Sheets-Sheet l ENCAPSULATION DIE CASTING 0F WINDLNGS, 0F CORES LEADS AND TERMINALS DIE CAST METAL INTD GRDOVES MOLD ENCAPSULANT WITH GROOVES (b) REMOVE METAL ELAsII TEST (b) REMOVE MOLDING FLASH (d) REWORK REJECTS ASSEMBLE MODULES FAG. 3A 15 I6 3 B F 2 INVENTORS KENDALL cLARK BY wILLIAM A. KLEIN KARL E. HERRMANN AM; aim/ /"A TDRNEY Nov. 4, 1969 K. CLARK ET AL. 3,477,051

DIE CASTING OF CORE WINDINGS Filed Jan. 15, 1968 4 Sheets-Sheet 4 0 D E e H i M 216 lllllllllllllllll llllllllllllllll lllllllllll United States Patent U.S. Cl. 33665 19 Claims ABSTRACT OF THE DISCLOSURE The windings, connecting leads and terminals for a magnetic component, such as pulse transformer or inductance, comprising an annular core, are produced by die casting metal into grooves formed in a molded plastic encapsulant which surrounds the core.

The technique of surrounding the core with a plastic encapsulant including forming the receiving grooves or channels in the encapsulant reduces the handling required in the manufacture of pulse transformers and the like and avoids the need for forming grooves in the ferrite or ceramic material of which the core is composed. Furthermore, it permits compensation of the dimensional variations between cores and enables simplification of the die structures for fabricating the windings.

BACKGROUND, SUMMARY AND OBJECTS OF THE INVENTION This invention relates to an improvement in the manufacture of ferromagnetic devices, and more particularly, to the fabrication of annular bodies or magnetic components having suitably disposed windings and adapted for use in pulse transformers, memory elements, and the like.

The present invention is more particularly concerned with the fabrication of inductors and transformers comprising toroidal cores, usually composed of materials, such as ceramic and ferrite, respectively, surrounded by windings. The invention is also concerned with a technique for so fabricating these devices that they are immediately ready for application, in the form of pulse transformers and the like, as components in electrical circuits. The technique includes encapsulating the cores and forming not only their essential windings, but also the connections therefrom to appropriate terminals, which terminals may also be concurrently formed during the process. All this may be accomplished at a very high production rate of the order of several thousand units per hour.

In order to provide the man skilled in the art with some background for an appreciation of the present invention, reference may be made to U.S. Patent 3,319,207 whichdiscloses a form of magnetic component which basically comprises a grooved toroidal ferrite body including a metal filling in the grooves so as to define a helical winding for the toroidal body.

The essential technique of U.S. Patent 3,319,207 has as its fundamental objective the provision of an improved component in which the winding or coil on the magnetic core does not have to be produced by any winding operation such as are encountered when ordinary wire is to form the coil. Although the described technique gets away from the difficulty stemming from the requirement that the coil be laboriously wound, it does not provide the answers for developing a fully automated, high production approach to forming the magnetic transformer units. In other words, that technique leaves unfulfilled the objectives of a significant reduction in the handling of magnetic cores and, also that they be provided in a 3,477,051 Patented Nov. 4, 1969 ice configuration that may be readily processed in large volume.

It is a primary object, therefore, of the present invention to reduce significantly the handling operations required in the manufacture of annular magnetic components.

Another basic object is to eliminate the necessity of forming grooves or channels in the annular core itself, that is to say, to avoid the necessity of abrading, cutting, or otherwise creating, the grooves in the ferrite or ceramic material of which the magnetic core is composed. It should be noted that, particularly in the case of ferrite material which is most commonly used for magnetic cores, such material is extremely brittle, and great care must be exercised in its handling. Also, this ferrite material is a conductor, being of sintered zinc-manganese iron composition. Consequently, the windings must be electrically insulated from the ferrite core.

Briefly stated, then, the present invention provides a magnetic transformer construction and an encapsula: tion method which allows for the fabrication of windings and of the connections, which extend from the windings on the core to the usual terminals or pins for a pulse transformer or the like. More specifically, the present invention envisions a ferrite core encapsulation technique, according to which the entire windings, and where included, also the connections and/or terminals are formed in a unitary or integral manner, preferably by means of die casting, thereby enabling the production of the magnetic components on a high-volume basis. Thus, the die casting technique for forming the windings and connections enables the turning out of extremely small magnetic elements at an extremely rapid rate.

In accordance with a more specific feature of the present invention it is contemplated that the magnetic core be encapsulated with a plastic and that grooves or channels be so molded therein as to conform with the size of the conductors that will define the windings, connections and/or terminals for the magnetic component. Thereafter, metal is die cast into the grooves or channels formed in the plastic.

It will be appreciated that the notion of having the core completely encased or encapsulated with plastic not only enables the avoidance of cutting of the typical ferrite body, which as noted before is extremely brittle, but concomitantly there is avoided the production of a turbulent flux path which leads to eddy currents and the consequent generation of excess heat which can change the magnetic characteristics of the magnetic element. Thus, in contrast, the magnetic component produced in accordance with the technique of the present invention has the grooves formed solely in the encapsulating plastic surrounding'the core and, consequently, the foregoing disadvantages are obviated.

Moreover, the novel plastic-encapsulation arrangement also allows for making up for large variations in size of the cores themselves that results from the sintering processing of the cores. In other words, it is no longer required that the cores be matched up to very strict tolerances but they can vary widely in dimensions and the variation can be compensated by the fact that the core is to be encapsulated with a plastic which appropriately and automatically is varied in the plastic molding operation so as to bring the final or overall dimensions of the-encapsulated ferrite body to the required values. Thus, fromanother aspect, the present invention effectively provides a solution to the difliculties normally attendant the di mensional tolerance requirements on the magnetic cores. The cores no longer have to be ground down to size and very closely matched before they can be put into production line.

the

In another aspect, the present invention provides a novel technique for the final stages in the formation of the windings on the magnetic core. As noted before, the metal which defines the windings is die-cast into the grooves that have been formed in the aforementioned plastic encapsulant. However, there inevitably remains some flashing, that is, material which spans the spaces between adjacent grooves. It is, of course, necessary that this flashing be removed. This accomplished in accordance with the present invention by simply immersing the entire assembly of the encapsulated core and its carrier plate into an etchant that will act to remove this metal flashing. This is accomplished on a time dependent basis, that is to say, the extremely thin flashing will be eaten away in a very short time interval but the metal that has been die-cast into the grooves will remain substantially unaffected.

In yet another aspect, the present invention involves what may be termed a unitary carrier concept. Such concept is amenable, or may be adapted, to automatic manufacturing techniques and thereby to the rapid formation of multi-core modules.

' Thus, the present invention, considered as a technique of fabricating magnetic components, also provides in modification of the invention the features of unitarily molding a plastic carrier plate at the same time and as an integral part of the plastic encapsulant for the core itself. In other words, a unitary carrier is envisioned so that the units may thereafter be very readily processed. The plastic carrier plate is provided with a set of balls or the like, on one end, and a set of receiving sockets on the other end. These are employed so as to join individual carrier plates together so that there is formed at a pre determined stage during the manufacturing processes a carrier strip and thereafter at the product stage, there may be formed a module, typically constituted by four pulse transformers hinged and linked together in any suitable manner such as by ball and socket joints.

Recapitulating, the complete method of the present invention may be viewed, in essence, as comprising the following fundamental steps: the encapsulation of annular magnetic cores by the molding of a grooved plastic encapsulant to surround same, and the die casting of the requisite windings, leads and terminals into those grooves in the plastic encapsulant. More specifically, the encapsulation of the cores involves the step of completely encasing the core with a ninsulating, plastic encapsulant and so molding the encapsulant that it is provided with grooves which completely define the helical path or paths for receivingthe metal for the windings. Inevitably, there results some plastic flash, that is, material which spans the desired gaps between the predetermined grooves, and this material, of course, must be removed. Production techniques have been developed whereby the plastic flash is removed by grit'blasting on a conveyor belt.

Comprehended as added features to the present invention are optional processing steps of electrical testing of the magnetic components and their assembly into packages or modules which consist of a plurality of magnetic devices assembled in desired configuration. Yet another step 'is the reworking of the rejects, that is, units that do not meet the imposed tests. It should be particularly noted here that-the present invention lends itself well to the reworking of rejected units. In other words, the failure rate when the technique of the present invention is followed is extremely low and this is for the reason that those units that do not come up to specifications do not have to be discarded, but are given a second chance so to speak. They are simply put back in the line and are reprocessed and brought to a satisfactory state.

Although only a brief description has been given here of the most fundamental aspects of the present invention, there will be provided hereinafter very specific examples of the modes of adapting the concepts of the present JIIVGRUQH to a ghcale p srluctian op ation vt4 Thus, the advantages of the present invention will be made manifest and it will be appreciated that the process set forth comprises a fully integrated atuomatic and feasible manufacturing method.

It should be particularly noted here that the use of the grooves in the encapsulant for the annular core is effective to reduce the die costs substantially. Because the grooves in the plastic encapsulant, in effect, form part of the die, the need is obviated for a conventional die, that is, a steel briquetting die with a complicated slotted pattern therein employed heretofore for forming cameo conductor patterns. The invention also eliminates a high wear rate inherent in conventional dies due to abrasive factors of ferrites. It will also be appreciated that with the notion of the plastic encapsulant there is brought about much greater versatility in the design configuration. Thus, it is not necessary to redesign the entire die apparatus in the event of a desired change in the winding configuration. Rather, it is only necessary to re-form the mold for the plastic encapsulant in the new pattern desired. Also, it will be understood that the die life is greatly increased because of the foregoing considerations.

Other advantages flow from the feature or concept of having the carrier plate as an integral part of the total housing. This feature contrasts, for example, with techniques previously known in the art and avoids the necessity for fabricating a carrier strip as a completed entity before commencing the die casting procedures. In other words, this further feature of the present invention eliminatesthe need to feed the plates that will form the base member for the completed units as a separate entity, and to feed the cores as another separate entity into the die casting apparatus. Rather, the carrier plate, with its own specially formed grooves for the reception of interconnecting leads, and the plastic material forming the encapsulant for the core itself, are all molded together in one operation so that there results a one-piece or unitary carrier which inherently furnishes the required support for the encapsulated core and includes all the required grooves and holes into which and through which the metal will be cast in the die casting apparatus to form the finished article.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow diagram of What may be regarded as the more basic steps in accordance with the process of the present invention.

FIG. 2 is an elevation view of a plastic molding apparatus for forming an encapsulated core unit in accordance with a first embodiment of the present invention.

FIGS. 3A and 3B are cross-sectional views of the plastic mold per se.

FIG. 3A illustrates the mold in the open position with a magnetic core being inserted therein, and FIG. 3B illustrates the mold in the closed position.

FIG. 4 is an enlarged perspective view of an encapsulated core unit as produced by the apparatus of FIGS. 3A and 3B.

FIG. 5 illustrates the various stages just prior to and during the die casting operation according to the first embodiment.

FIG. 6 is an enlarged perspective view of a completed magnetic component, such as a pulse transformer, according tothe first embodiment.

FIG. 7 is an enlarged sectional view of a typical supporttab, taken on the line 7-7 of FIG. 6.

FIG. 8 is an enlarged sectional view of a typical connecting lead and terminal arrangement, taken on the line 8-8 of FIG. 6.

FIGS. 9A and 9B are cross-sectional views of the plastic molding apparatus for forming a unitary carrier type of encapsulated core unit in accordance with the second embodiment of the present invention.

FIG. is an enlarged perspective view of an encapsulated core unit in accordance with the second embodiment.

FIG. 11 is a bottom plan view of a modified encapsulated core unit, which is similar to the one previously depicted in FIG. 10.

FIG. 12 depicts a typical winding pattern for the encapsulated core unit shown in FIG. 11.

FIG. 13 illustrates the formation of the windings, interconnections and terminals on an encapsulated core unit, particularly illustrating the die casting apparatus for this purpose.

FIGS. 14A and 14B depict two conditions for the magnetic component following the die casting operation; before and after etching respectively.

FIG. 15 is a perspective view of a group of interconnected pulse transformers in what is termed a quad module.

DESCRIPTION OF PREFERRED EMBODIMENTS First embodiment Referring now for the moment to FIG. 1, the essential operations according to the technique of the present invention are graphically indicated. In particular, considering the technique or process in the order of its fundamental steps, it will be seen that the first basic step is that of encapsulation of the annular cores. This step is carried out in the apparatus illustrated in FIGS. 2, 3A and 3B, thereby to produce the encapsulated core unit as shown in FIG. 4.

Referring specifically to FIG. 2, there is illustrated a fairly conventional plastic molding apparatus 10. The elements of this apparatus, outside of the mold itself, are well-known in the art. They are seen to include a hydraulic cylinder 12 and a piston 13 for forcing plastic material into a mold 14. Also included are conventional upper and lower platens 15. A chamber 16 in the upper platen communicates with the passageways 18 in the upper mold half 14a. This allows flow of the plastic material into the mold cavity 20 as the piston 13 is driven down.

The core itself, that is, in its pristine state before the plastic encapsulant has been molded around it, is designated 100 and, as indicated by the arrows in FIG. 3A, this core 100 is inserted into the lower part 14b of the mold.

The mold cavity 20 in the lower mold part 14b is generally annular in form for reception of the illustrated annular core. The surfaces of the cavity are complementarily formed with respect to the desired configuration for the encapsulated core unit 110 as shown in FIG. 4. That is to say, the side walls and the bottom of the cavity 20 are provided with a series of projections or protuberances 24 which define the corresponding side and bottom grooves 120a in the plastic encapsulant 120 surrounding the core 100 (FIG. 4). Also, the upper mold part 14a is provided with the necessary projections or protuberances 26 so as to define the corresponding top grooves 120a.

Referring now to FIG. 3B, it will be understood that, when the two parts of the mold are brought together and the plastic material is forced into the mold 14, the spaces remaining between the core 100 (as it is positioned within the lower part 14b of the mold) and the surfaces of the cavity 20 will be completely filled with the plastic. Consequently, the core is completely surrounded by the plastic encapsulant 120. For proper support and positioning of the core, in the mold, chairs 27 are provided. Because of the presence of these chairs 27, spaced recesses 12% result in the encapsulant 120.

For the purposes of the present invention it has been found that a thermosetting plastic is the most useful type of material and that an epoxy resin is most suitable for serving as the encapsulant 120 for the magnetic core 100. The epoxy resin, of course, is an insulator and thus the required function of insulating the conductive ferrite core from the windings 250 of FIG. 6 is also served by this material. The temperature that is selected for use in the plastic molding apparatus is of the order of 340 F. and preferably is selected to be between 290-360 F. Although the drawings and the description which follows exemplify a single cavity mold, for the sake of simplicity in explaining the principles of the invention, it will be understood that multiple cavity molds can be utilized. It will be appreciated that the molding operation for producing the encapsulation of the cores 100 affords a very significant advantage in compensating for variations in the dimensions of these annular ferrite cores. Accordingly, it is no longer necessary that all of the magnetic cores that are to be encapsulated be first rigidly inspected and then by some means, such as by grinding, be brought to within very precise tolerances. Rather, the cores can be brought within wide dimensional limits directly from sintering operations, and thereafter supplied to the molding apparatus for performance of the encapsulation operation. The encapsulated core units 110, as they emerge from the molding apparatus, will perforce be close to being identical since they are all molded in the same or dimensionally similar molds.

Because of the complementarily formed molding surfaces within the mold 14, the grooves 120a are formed as has been noted before. These grooves are serially connected so as to form continuous helical paths. Subsequently, when the metal that is to form the windings is die-cast into them, there will be created helical windings completely surrounding the annular core 100.

It will be understood that the finished molded article in the form of plastic encapsulated core unit does not emerge from the molding apparatus exactly as shown in FIG. 4. Thus, it is inevitable in the molding operation and particularly because of the provision of the grooves 1200c that there is concomitantly produced a molding flash. However, this molding flash is very easily removed in a manner well-known in the art to produce the finished encapsulated core unit 110.

After removal of this molding flash, the plastic encapsulated core units 110 are brought to the die casting station, that is, to the station as represented by the box in FIG. 1 labeled DIE CASTING OF WINDINGS. At the station, in addition to the operation of forming of the helical windings for the encapsulated magnetic cores, if desired there can be also formed in this unitary manner the terminals and/or the connections from the windings to appropriate terminals. Further, it should be noted that at the die casting station there is performed the step of mounting and supporting the core on a plastic carrier strip so that the core can thereafter be utilized in a circuit board or integrated circuit type of package.

Referring now to FIG. 5, there is illustrated here, in greatly simplified fashion, a production line of magnetic components. Thus, it will be seen, looking at the right, that .a carrier strip 200, which consists of a plurality of joined carrier plates 210, is in the process of being fed into' the die casting machine (not illustrated here). This carrier strip 200 usually consists of a 50-yard length or so of the carrier plates 210. Thus, the strip of plastic plates can be very easily rolled up in a coil or the like andcan be fed in this form into the die casting machine.

The point A represents the point at which the carrier strip enters the die casting machine. Concurrently with the insertion of one of the carrier plates, a corresponding encapsulated core unit 110, having been formed as already described, is also oriented and fed into the die castingmachine.

The machine or apparatus for performing the die casting operation, that is, for die casting the windings and interconnections, will be described hereinafter in connection with a second embodiment of the present invention. It is considered sufficient here merely to note that, for the particular construction of this first embodiment, a suitable die casting die is provided with the requisite grooves or slots for producing the terminals 220 and the support tabs 230. The metal which is to form the core windings, the interconnections, etc. is forced into the die under sufficient pressure so that the flowing metal is able to penetrate into all the spaces defined by the grooves and the die surfaces.

It will be noted that in FIG. there is shown an inverted arrangement, Whereas in FIG. 6 a completed unit is shown in the up position, that is, with the encapsulated core unit 110 above the plane of the carrier plate 210.

The carrier plates 210 are typically formed, at least in this embodiment, of Mylar plastic material and thus are extremely flexible. Each of the carrier plates 210 is provided with a large central opening 210a for enabling proper positioning of the encapsulated core unit 110, and a pair of holes 21% for registering with die pins. A group of holes 210C is arranged near the edge of the plate 210 for enabling the anchoring of the interconnecting leads 240 to the plate. Also provided is a series of holes 210d spaced around the opening 210a for proper anchoring of the support tabs 230. Each plate 210 has a means for attaching to the next succeeding and to the previous carrier plate; thus, it will be seen in FIGS. 5 and 6 that a typical carrier plate 210 is so formed as to have a ball and socket joinder means, there being a plurality of balls 212 at one end of each carrier plate and a corresponding plurality of sockets 214 at the other end. Consequently, the carrier strip is very readily put together, that isthe plates 210 can be formed in the long strip 200 prior to the die casting operation. The carrier strip is suitably indexed so that each of the plates 210 can be properly and progressively fed into position in the die casting apparatus. In other Words, the individual plates 210 may be separated from the strip 200 as it approaches point A, and then fed one-by-one, by suitable means not shown, and placed accurately in position within the die; then'the core unit 110 is firmly fixed into position, the die is closed and the metal is forced into the die so as to create the windings 250 about the core, the tabs 230, the interconnecting leads 240 and, if called for, the terminals 220. Alternatively, the continuous strip 200 may be led into the die casting machine A, as illustrated by FIG. 5, Without separating the individual plates 210.

It will be understood that a great variety of devices can be produced in accordance with the encapsulationdie casting technique already described. Thus, a typical device application for the technique would be the formation of a pulse transformer which is a device requiring a ferrite core or the like and a plurality of windings. These windings are, of course, produced in the aforedescribed manner, the particular winding pattern that is desired for a pulse transformer being first selected and then implemented in the molding operation by the creation of the appropriate grooves in the encapsulant. Thereafter, the metal is diecast into the grooves to effectuate the given winding pattern. Thus, as one example, a center tapped primary winding is selected for implementation and a single winding secondary is also selected. Such a winding configuration would entail the interconnections to the five terminals 220 as seen in FIG. 6.

In the die casting operation, core unit 110 and the carrier 210 are effectively sandwiched between two heated die casting die sections, and a clamping force of approximately 1000 pounds is applied. The die is usually heated to a temperature of approximately 440 F., depending on the metal used. This preferred temperature was selected after numerous attempts at die casting with varying temperatures. It was found that with lower temperatures, for example, down to 410 or so, problems resulted from the fact that metals solidified at the entrance to the die or the flash produced was too great or the metal moved too rapidly or the die did not fill properly. It should be noted, however, that the experiments commented on above related to pecific compositions or alloys that we used and that these temperatures would not apply to other compositions.

In connection with the point emphasized above with respect to the varying compositions of metals that have been tried, it should be especially noted here that the selection of the particular metals and similar selections are important to a full realization of the results achievable in applying the principles of the present invention. Specifically, a tin-silver alloy was found to be the best composition in our experiments. The percentage of silver was varied from about 5% upward to about 15%.

It should benoted that severe problems attend these attempts to get metal to flow through the very small cross: sections that are involved. The inner grooves in the plastic encapsulant into which the metal is to be die cast are of the order of only 6 x 4 mils, that is, 6 mils deep and 4 mils wide. (One mil is .001 inch.)

The techniques of the present invention have overcome the problems associated with such small cross-sections and have also overcome the related problems of plastic and metal flash, and the problem, previously noted, of excessive die costs. Therefore, in its more specific aspects, it will be appreciated that the present invention furnishes important solutions to the problems attendant the die casting of metal windings on miniature magnetic components.

Merely by way of example, one specific procedure that has been adopted in this connected is the following: The tin-silver alloy is melted down on a hot plate at a temperature of approximately 600 F. and the so-called hot pot is also preheated on the hot plate. When the proper temperature has been reached for the hot pot it is clamped to the die and the molten tin-silver alloy poured into the pot, and thereafter, an air driven piston forces the molten alloy into the die thereby filling the core cavities, that is to say, the cavities defined by the grooves previously formed. It will thus be apparent how simply achieved is the die casting of the metal into these grooves. When the metal solidifies the die is taken apart and the magnetic component may be removed from the die. The magnetic component 260, in the form of a pulse transformer or the like, is seen in its finished state in FIG. 6.

Second embodiment Referring now to FIGS. 9-15, there is illustrated a second embodiment of the technique of the present invention and another form of magnetic component fabricated by following such technique. In this embodiment, in contrast with the formation, already described, of the component of FIG. 6, the feature of molding a unitary carrier is implemented. Thus, at the encapsulation or molding stage, the entire housing for the core is formed in a single operation such that the portion of the housing previously denominated as a carrier plate 210- is formed integrally with the plastic encapsulant which immediately surrounds the core. Consequently, all of the housingis constituted of epoxy resin or similar material. In view of this, the numeral 300 is used to designate this unitarily or integrally molded unit. To produce this encapsulated unit 300 the plastic mold, illustrated in FIGS. 9A and 9B, is designed to have a configuration which is complementary to the configuration of the unit illustrated in FIG. 10. This means that holes must be formed that penetrate through the carrier plate 210 thereby to allow for continuity in the pattern of the wind ings that surround the core 100. These holes are best seen in FIG. 11 and are designated by the numeral 216.

As was the case with the component produced by the first embodied technique, that is, the component of FIG. 6, it is necessary again to provide for the formation of the interconnection pattern from the windings surrounding the core to the terminals or other connectors that are used for circuit-connecting purposes.

Comparison of FIGS. 3A and 3B with FIGS. 9A and 9B will make quite apparent the differences in the mold that become necessary in order to form the unitarily 9 molded unit of FIG. 10: In FIGS. 9A and 9B the same numerals have been employed to designate the parts previously shown in FIGS. 3A and 3B. The cavity 20 (FIG. 9A) is now expanded to accommodate the influx of plastic material necessary to form the base or carrier plate 210. The core 100 is again shown in position within the lower half 1412 of the bold. The passageways 18 are now designed in slightly different fashion but have the same essential purpose; they communicate with the mold cavity 20 by means of a standard runner system 22 with a small, easily removable gate 23. Such a system would be applicable to multi-cavity, high production molding.

It should be particularly noted in FIG. 9A that the projections or protruberances 24 as they extend axially in defining the grooves in the encapsulant are so fashioned that they produce the required holes 216 in the carrier plate 210. Also, the chairs 27 are again provided to support and center the core 100.

As best seen in FIGS. 10 and 11, the required grooves for the reception of the interconnecting leads, that is, the leads which extend from the windings to appropriate terminals or pins, are also defined by the same molding operation. Certain of these grooves are designated 218 and they are situated on the bottom of the carrier plate 210. A groove 217 is also provided on the top of the plate. The encapsulated core units themselves 300 are identical in FIGURES l and 11; however, the means for joining a plurality of units 300 is modified somewhat in FIGURE 11. Thus, the joinder means shown there includes several balls 213 at one end, which are received in recesses 215 at the opposite end of a plate 210'.

A typical winding pattern that may be provided for a pulse transformer or the like, is illustrated in FIG. 12. A quad filar is provided; two of the windings 320- and 322, are connected in series between the terminals B and D and constitute a secondary for the pulse transformer. The other two windings 324 and 326, are connected in series to the terminals marked A and E, and constitute the primary. This primary is center-tapped; that is, the point between these windings is connected to the terminal marked C. The implementation of the winding pattern of FIG. 12 in the grooves 120a of the encapsulated unit 300, and in the grooves in the carrier plate 210 thereof, may be appreciated by reference to FIG. 11. In this figure, for the sake of simplicity, only the primary winding has been traced out by the use of dotted lines. This can be followed by means of the arrows L, M, N and P shown thereon.

The die casting operation for the second embodiment of the present invention and the ancillary steps following the actual die casting will be understood by reference to FIG. 13. It will be appreciated for reasons already explained that the separate carrier strip, in the form illustrated in FIG. is no longer necessary. A plurality of the individual, unitary molded, encapsulated cores 300 are linked together in a chain or strip of elements for ease in handling and adaptation to automatic processing, for the second basic step, that is, the step of die casting. The individual units 300 are broken away from the continuous strip and are automatically fed into the die casting die 400 by suitable indexing means not shown. Alternatively, the continuous strip may be fed into the die casting machine without separation into individual parts, similar to the method described for the first embodiment.

The metal in the form of a silver-tin composition is injected into the die by means of the conduits 410, and pressure is brought to bear so as to result in forcing the silver-tin composition into the grooves that define the windings. Likewise, the metal is forced into the grooves 217 and 218 for producing the interconnecting leads. Moreover, as is usually preferred, the die 400 is so formed that the terminals or pins 220 are also formed by the influx of the silver-tin alloy.

The salient advantage that is best appreciated at this juncture is the extreme simplicity of construction for the die 400. This is for the reason that the metal is being forced into the grooves already formed in the encapsulant rather than into the slots or grooves in a steel die cavity. Thus, only a smooth bored, annular or toroidal cavity is required within the die 400-at least for the core portion of the unit. It will thus be apparent that a wide variety of winding patterns can be accommodated without the need to change the cavity configuration again, since only the grooves in the plastic encapsulant need be changed as the winding pattern is altered.

The core unit as it emerges from the die casting apparatus is designated 500 and may be seen to the left in FIG. 13, and also, in FIG. 14A. It will be noted that the encapsulated core and the supporting plate 210 may be completely or partially covered by metal. This is due to the fact that a metal flash may have been formed, which is to say that the metal not only penetrates into the grooves but may also completely or partially bridge the spaces between grooves. Likewise, the metal may completely or partially penetrate over the available spaces or openings in the plate 210. Hence, it becomes necessary to remove this metal flash to avoid electrical shorting between windings or leads. It will also be noted that the metal flash is relatively thin compared to the metal in the plastic grooves.

The thin metal flash is removed in accordance with another feature of the present invention. This metal flash removal step has clearly been indicated in FIG. 1 as part of the overall technique. The flash is removed simply by immersing the entire unit 500 in an etchant that will act to eat away the thin coating or flash. Preferred etchants for this purpose are aqua regia or nitric acid. The etching operation is on an empirically determined time basis, that is to say, the etching is continued until the very thin metal flash coating is removed leaving only the desired thicker metal windings and interconnections.

The finished article, that is, the transformer unit as it will be used in an electrical circuit is shown in FIG. 14B and is designated 600. The metal conductors 650 are clearly seen radially and axially extending within the grooves to define the helical windings for the core.

The other steps that are performed following the etching of the flash are the electrical testing of the units and their assembly into desired modules or the like. The units 600 have been so formed that they may be readily fitted together by means of the ball and socket interconnections. Thus, a quad module in a box-like configuration 700 as shown in FIG. 15 can be readily assembled. After assembly into the quad module this module is dlpped into liquid plastic up to but not covering the terminals 220. A subsequent oven baking polymerizes the liquid plastic into a hard resin. The hard resin freezes the ball and socket hinges 212 and 214 into a rigid quad module structure, and provides an electrical insulating coating over the windings 650', and leads 217, 218.

If, on testing certain of the units 600, these are found to be defective, such rejects can be very easily reworked and hence the yield that is obtainable by the technique of the present invention is extremely high. This may be appreciated by considering, as one example, the situat1on where an electrical short is detected. In such case the unit 600 is sent back to the etching bath to have its die cast metal completely removed. Alternatively, the metal may be melted out on a heated vibratory table. This merely turns the unit 600 to its former state and it becomes just another encapsulated core unit 300 which can be placed back in the line and have its metal windings and interconnections re-cast.

Some of the transformer units 600' may have had defective plastic encapsulation. The plastic can be removed by solvent action or burned off. The bare ferrite core can then be re-eneapsulated in plastic and placed back in the line to have its metal windings and interconnections re-cast,

Specific implementation of inventive principles In order to provide a man skilled in the art with a detailed set of specifications for enabling him to put the present invention into practice on a production scale, a manufacturing process sequence is herewith shown in outline form. This process sequence is particularly adapted to the manufacture of die cast pulse transformers in high production quantities.

1.0 Core encapsulation 1.1 Move cores and plastic to encapsulation station 1.2 Core checking equipment 1.2.1 Load cores into feed bowl .2.2 Check outside diameter .2.3 Check inside diameter 2.4 Check thickness 2.5 Magnetic check 2.6 Discard reject cores 2.7 Offload accept cores into move box 1.2.8 Move accept cores to encapsulation station 1.3 Plastic briquetting equipment (mechanized, periodically attended by floor technician) 1.3.1 Load plastic into hopper 1.3.2 Form plastic briquettes 1.3.3 Off load briquettes into move box 1.3.4 Move briquettes into encapsulation press area 1.4 Briquette preheating equipment (attend by transfer press operator) 1.4.1 Place briquettes in preheat 1.4.2 Off load briquettes onto feed chute or platen 1.5 Mold loading equipment (core loading fully mechanized, briquette loading manually) .5 .1 Load cores into vibratory feeder .5 .2 Load cores into shuttle .5 .3 Move shuttle into position over mold .5.4 Offload cores .5.5 Remove shuttle .5. E

1 1 l. l. 1. l.

6 Close mold ncapsulate cores [(4 transfer presses, 3 operating, v1 spare) (32 cavities)] 1.6.1 Perform 1.4.2 1.6.2 Transfer mold 1.6.3 Repeat 1.5.2 while plastic is curing (automatic loading of cores) 1.6.4 Open press 1.7 Unload and clean mold 1.7.1 Eject plastic encapsulated cores .7.2 Eject gates, runners, scrap .7.3 Air blast mold 7.4 Visually check mold 7.5 Spray mold with release (as needed) 7.6 Repeat 1.5.3-1.6.3 1.7.7 Separate gate work from parts 1.7.8 Sample inspection parts under scope 1.7.9 Repeat 1.6.4-1.7.9 2.0 Remove molding flash 2.1 Load encapsulated cores into vibrational feeder bowl 2.1.1 Feed encapsulated cores into sand blasting unitremove flash 2.1.2 Clean encapsulated cores with air 2.1.3 Load encapsulated cores into trays using tray loader 2.1.4 Sample inspect visually (3% A.Q.L.) 2.1.5 Move to shipping area 3.0 Move encapsulated cores to die casting station 4.0 Die cast windings, leads, and contact pads onto encapsulated cores 5.0 Clean pulse transformers (wash) 6.0 Remove die cast metal flash (automatic equipment) 6.1 Move pulse transformers in trays to flash removal area 6.1.1 Load trays into etch tank 6.1.2 Etch remove flash (in tray) 6.1.3 Rinse pulse transformer (in tray) to quad former) (205-203 and others go to stock) 8.0 Module assembly (same as alternative) 9.0 Rework 9.1 Rework D.C. shorts 9.1.1 Load trays of pulse transformers onto etching equipment 9.1.2 Rework process items 6.1.2 to 7.1.6

9.2 Remove die cast metal (over pulse vibratory feeder) 9.2.2 Load pulse transformers into trays using equipment of 2.1.5 (label and segregate through process 9.0 to 9.2 to prevent second rework) 9.2.3 Repeat operations 4.0 to 7.1.6

9.3 Salvage cores (all rework rejects) 9.3.1 Remove metal as per 9.2.1

9.3.2 Remove plastic encapsulant from around core (in solvent bath) 9.3.3 Rinse cores 9.3.4 Dry cores 9.3.5 Move cores and reprocess While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. An electrical component comprising an annular body, including an annular magnetic core and a continuous unitary plastic encapsulant completely surrounding and sealing said annular core; a series of spaced channels formed axially and radially in said plastic encapsulant and interconnected so as to define at least one flow path for metal for establishing a helical winding around said annular core, metal conductors disposed in said channels to define said helical winding, said metal conductors being spaced from said core by said encapsulant.

2. An electrical component as defined in claim 1, in which said annular core is composed of ferrite material.

3. An electrical component as defined in claim 1, in which said channels are constituted by grooves and wherein said core has smooth radially surfaces and smooth inner and outer peripheral surfaces, said plastic encapsulant surrounding the core so as to have its corresponding surfaces located a predetermined distance outwardly from the surfaces of the core, the grooves in said encapsulant extending inwardly to a depth substantially less than said predetermined distance.

4. An electrical component as defined in claim 3, in which said plastic encapsulant is an epoxy resin, and in which the grooves in said plastic encapsulant have dimensions of the order of 6 mils in depth and 4 mils in width.

5. An electrical component as defined in claim 1, further including an individual carrier plate for said core and means afiixing the encapsulated core to said plate.

6. An electrical component as defined in claim 5, wherein said plate is constituted of plastic.

7. An electrical component as defined in claim 5, wherein said carrier plate is integral with the plastic encapsulant surrounding the core, and is perpendicular to the axis of the core as an extension of one surface of the plastic encapsulant.

8. An'electrical component as defined in claim 5, further including means for joining said-.carrier plate with identical plates, including balls at one end of said plate and receiving sockets at the other end.

9. An electrical component as defined in claim 5, wherein said carrier plate is provided with indexing holes, and with holes for anchoring interconnecting leads and support tabs to said carrier plate.

10. An. electrical component as defined in claim 9, further including said interconnecting leads and said support tabs.

11. An electrical component as clefined in claim 10, further including terminals extending fromsaid carrier plate as an integral part of said leads.

12. An electrical component as defined in claim 11, wherein said terminals comprise pins connected to said leads.

13. A pulse transformer comprising an annular magnetic core and a continuous unitary plastic encapsulant completely surrounding and sealing said annular magnetic core; a series of spaced channels formed axially and radially in said plastic encapsulant, and interconnected so as to define a plurality of flow paths for metal for establishing helical windings around said annular magnetic core; and metal conductors in said channels, spaced from said core by said encapsulant, forming at least a primary and a secondary winding for said transformer.

14. A pulse transformer as defined in claim 13, in which said annular magnetic core is composed of ferrite material.

15. A pulse transformer as defined in claim 13, in which said channels are constituted by grooves and in which said annular magnetic core has smooth radial surfaces and smooth inner and outer peripheral surfaces, said plastic encapsulant surrounding the core So as to have its corresponding surfaces located a predetermined distance outwardly from the surfaces of the core, the grooves in said encapsulant extending inwardly to a depth substantially less than said predetermined distance.

16. An electrical component as defined in claim 15, in which said plastic encapsulant is an epoxy resin, and in which the grooves in said plastic encapsulment have dimensions of the order of 6 mils in depth and 4 mils in width.

17. A pulse transformer as defined in claim 15, further including a carrier plate and a means for affixing the encapsulated core to said plate.

18. A pulse transformer as defined in claim 17, in which said plate is constituted of plastic.

19. A pulse transformer as defined in claim 17, in which said carrier plate is integral with said plastic encapsulant surrounding the core, and said plate is perpendicular to the axis of the core, as an extension of one surface of the plastic encapsulant.

References Cited UNITED STATES PATENTS 2,826,747 3/1958 Carey 336229 XR 2,982,888 5/1961 Whearley 336-208 XR 3,008,108 11/1961 Baker et a1 336-229 XR 3,287,795 11/1966 Chambers et al.

3,316,517 4/1967 Ellin 336198 XR 3,319,207 5/ 1967 Davis 336229 3,377,699 4/ 1968 Dinella et a1 33696 XR 3,390,308 6/1968 Marley 174-68.5

LEWIS H. MYERS, Primary Examiner T. J. KOZMA, Assistant Examiner U.S. Cl. X.R. 

